EP4198416A1

EP4198416A1 - Refrigeration machine

Info

Publication number: EP4198416A1
Application number: EP21875130.3A
Authority: EP
Inventors: Yuki Namba; Takahide Ito; Atsushi Enya; Toshiyuki Ishida
Original assignee: Mitsubishi Heavy Industries Thermal Systems Ltd
Current assignee: Mitsubishi Heavy Industries Thermal Systems Ltd
Priority date: 2020-09-29
Filing date: 2021-09-09
Publication date: 2023-06-21
Also published as: JP7391811B2; EP4198416A4; JP2022055607A; WO2022070828A1

Abstract

This refrigeration machine comprises: a low temperature cycle having an evaporator which performs heat exchange between air inside a refrigeration chamber and a first refrigerant, a first compressor which compresses the first refrigerant and supplies the compressed first refrigerant to the evaporator, and a low temperature-side expansion valve which lowers the pressure of the first refrigerant that has passed through the first compressor; a high temperature cycle having a heat dissipator which performs heat exchange between outside air and a second refrigerant, a second compressor which compresses a second refrigerant and supplies the compressed second refrigerant to the heat dissipator, and a high temperature-side expansion valve which lowers the pressure of the second refrigerant that has passed through the heat sink; an intermediate heat exchanger which performs heat exchange between the first refrigerant flowing from the first compressor and the second refrigerant flowing from the high-temperature side expansion valve; and a gas injection circuit which is provided to at least one of the low temperature cycle and the high temperature cycle, and which supplies the refrigerant before compression to at least one of the first compressor and the second compressor, wherein the first refrigerant is a mixed refrigerant containing carbon dioxide and R32 refrigerant, and the second refrigerant is carbon dioxide.

Description

Technical Field

The present disclosure relates to a chiller. Priority is claimed on Japanese Patent Application No. 2020-163122 filed on September 29, 2020 , the content of which is incorporated herein by reference.

Background Art

In recent years, in the field of chillers, it is required to minimize a global warming potential (GWP) value. Therefore, there are often restrictions on the types of refrigerants that can be used. Specific examples of a refrigerant capable of realizing a low GWP include a refrigerant called R32 and carbon dioxide (refer to PTL 1 below).
On the other hand, in a case where such a low GWP refrigerant is used, an improvement in a cooling capacity of a chiller may be hindered. In particular, this effect is significant in a chiller in which a target temperature is an ultra low temperature of about -45°C to -70°C. Therefore, for example, measures such as increasing a compression ratio of a compressor used in the chiller can be considered.

Citation List

Patent Literature

[PTL 1] Japanese Patent No. 4543469

Summary of Invention

Technical Problem

However, in a case where the compression ratio is simply increased as described above, a discharge temperature of the compressor becomes excessively high, and there is a concern that a desired cooling capacity cannot be exhibited. As described above, there is an increasing demand for a chiller having an ultra low temperature cooling capacity while using a low GWP refrigerant.
The present disclosure has been made to solve the above problems, and an object thereof is to provide a chiller capable of achieving both a low GWP and a high cooling capacity.

Solution to Problem

In order to solve the above problems, a chiller according to the present disclosure includes: a low-temperature cycle including an evaporator that exchanges heat between an air in a freezing chamber and a first refrigerant, a first compressor that compresses the low-pressure gas-phase first refrigerant supplied from the evaporator, and a low-temperature-side expansion valve that lower a pressure of the first refrigerant that has passed through the first compressor; a high-temperature cycle including a condenser that exchanges heat between an outside air and a second refrigerant, a second compressor that compresses the second refrigerant and supplies the second refrigerant to the condenser, and a high-temperature-side expansion valve that lowers a pressure of the second refrigerant that has passed through the condenser; an intermediate heat exchanger that exchanges heat between the first refrigerant flowing from the first compressor and the second refrigerant flowing from the high-temperature-side expansion valve; and a gas injection circuit that is provided in at least one of the low-temperature cycle and the high-temperature cycle and supplies the first refrigerant or the second refrigerant before being compressed to at least one of the first compressor and the second compressor, in which the first refrigerant is a mixed refrigerant containing carbon dioxide and an R32 refrigerant, and the second refrigerant is carbon dioxide.

Advantageous Effects of Invention

According to the present disclosure, it is possible to provide a chiller capable of achieving both a low GWP and a high cooling capacity.

Brief Description of Drawings

Fig. 1 is a refrigerant circuit diagram showing a configuration of a chiller according to an embodiment of the present disclosure.
Fig. 2 is a cycle diagram of the chiller according to the embodiment of the present disclosure.

Description of Embodiments

(Configuration of Chiller)

Hereinafter, a chiller 100 according to an embodiment of the present disclosure will be described with reference to Figs. 1 and 2. As shown in Fig. 1, the chiller 100 includes a high-temperature cycle CH, a low-temperature cycle CL, an intermediate heat exchanger 10 connecting the high-temperature cycle CH and the low-temperature cycle CL, and a gas injection circuit 9. That is, the chiller 100 forms a cascade cycle type refrigeration circuit. A refrigerant (a second refrigerant described later) that exchanges heat with an outside air in the high-temperature cycle CH exchanges heat with another refrigerant (a first refrigerant described later) on the low-temperature cycle CL side at the intermediate heat exchanger 10. In the low-temperature cycle CL, heat is exchanged between an indoor air and the refrigerant.

(Configuration of High-Temperature Cycle)

The high-temperature cycle CH includes a high-temperature-side pipe P2, a second compressor 4, a condenser 5, a high-temperature-side expansion valve 6 (a high-temperature-side first expansion valve 61 and a high-temperature-side second expansion valve 62), and a high-temperature-side receiver 82. The high-temperature-side pipe P2 is a pipeline connected in an annular shape, and an inside thereof is filled with the second refrigerant. The second refrigerant contains only carbon dioxide.
On the high-temperature-side pipe P2, from an upstream side to a downstream side in a flow direction of the second refrigerant, the second compressor 4, the condenser 5, the high-temperature-side first expansion valve 61, the high-temperature-side receiver 82, and the high-temperature-side second expansion valve 62 are arranged in this order.
The second compressor 4 compresses a low-pressure gas-phase refrigerant supplied from the intermediate heat exchanger 10 to generate a high-temperature and high-pressure gas-phase refrigerant. The second compressor 4 is a so-called scroll rotary type two-stage compressor, in which a rotary compressor 41 is used as a low pressure side and a scroll compressor 42 is used as a high pressure side. The rotary compressor 41 and the scroll compressor 42 are, as an exception, coaxially connected to each other.
The high-temperature and high-pressure gas-phase refrigerant generated by the second compressor 4 flows into the condenser 5. The condenser 5 is provided outside a freezing chamber (a room to be frozen). In the condenser 5, heat is exchanged between the second refrigerant and the outside air. It is desirable that the outside air is forcibly sent to the condenser 5 by a fan (not shown). Accordingly, the gas-phase refrigerant is condensed in the condenser 5, and a high-pressure liquid-phase refrigerant is generated.
The high-pressure liquid-phase refrigerant passes through the high-temperature-side first expansion valve 61, the high-temperature-side receiver 82, and the high-temperature-side second expansion valve 62 in this order. The high-pressure liquid-phase refrigerant is reduced in pressure to a certain extent while passing through the high-temperature-side first expansion valve 61, and becomes a medium-pressure and medium-temperature liquid-phase refrigerant. This liquid-phase refrigerant is stored in the high-temperature-side receiver 82 and is separated into a gas and a liquid. The gas phase component is supplied to the second compressor 4 (specifically, a position upstream of the scroll compressor 42 on the high pressure side) through a high-temperature-side circuit 92 as the gas injection circuit 9. That is, the low-temperature second refrigerant (gas phase component) before being compressed is sent to the second compressor 4 through the high-temperature-side circuit 92.
The medium-temperature and medium-pressure liquid-phase refrigerant that has passed through the high-temperature-side receiver 82 passes through the high-temperature-side second expansion valve 62 and is further reduced in pressure to become a low-temperature and low-pressure liquid-phase refrigerant.
The low-temperature and low-pressure liquid-phase refrigerant that has passed through the high-temperature-side second expansion valve 62 flows into the intermediate heat exchanger 10. In the intermediate heat exchanger 10, heat exchange occurs between the second refrigerant in the high-temperature cycle CH and the first refrigerant in the low-temperature cycle, which will be described later. Specifically, heat exchange occurs between the high-temperature and high-pressure gas-phase refrigerant (first refrigerant) flowing through the low-temperature cycle CL and the low-temperature and low-pressure liquid-phase refrigerant (second refrigerant) flowing through the high-temperature cycle CH. Correspondingly, in the high-temperature cycle CH, the liquid-phase refrigerant flowing through the intermediate heat exchanger 10 increases in temperature and changes from a liquid phase to a gas phase.
The refrigerant that has become the gas phase after passing through the intermediate heat exchanger 10 is suctioned into the second compressor 4 again. In the high-temperature cycle CH, such a cycle is continuously performed.

(Configuration of Low-Temperature Cycle)

The low-temperature cycle CL includes a low-temperature-side pipe P1, a first compressor 2, an evaporator 1, a low-temperature-side expansion valve 3 (a low-temperature-side first expansion valve 31 and a low-temperature-side second expansion valve 32), and a low-temperature-side receiver 81. The low-temperature-side pipe P1 is a pipeline connected in an annular shape, and an inside thereof is filled with the first refrigerant. The first refrigerant is a mixed refrigerant of carbon dioxide and an R32 refrigerant. The R32 refrigerant is contained in the first refrigerant in a range of 16 wt% or more and 22 wt% or less. A component remaining therein is carbon dioxide.
On the low-temperature-side pipe P1, from an upstream side to a downstream side in a flow direction of the first refrigerant, the first compressor 2, the low-temperature-side first expansion valve 31, the low-temperature-side receiver 81, the low-temperature-side second expansion valve 32, and the evaporator 1 are arranged in this order.
The first compressor 2 compresses a low-pressure gas-phase refrigerant supplied from the evaporator 1 to generate a high-temperature and high-pressure gas-phase refrigerant. Similar to the second compressor 4, the first compressor 2 is a so-called scroll rotary type two-stage compressor, in which a rotary compressor 21 is used as a low pressure side and a scroll compressor 22 is used as a high pressure side. The rotary compressor 21 and the scroll compressor 22 are, as an exception, coaxially connected to each other.
The high-temperature and high-pressure gas-phase refrigerant generated by the first compressor 2 flows into the intermediate heat exchanger 10. In the intermediate heat exchanger 10, heat exchange occurs between the second refrigerant in the high-temperature cycle CH and the first refrigerant in the low-temperature cycle. Specifically, heat exchange occurs between the high-temperature and high-pressure gas-phase refrigerant (first refrigerant) flowing through the low-temperature cycle CL and the low-temperature and low-pressure liquid-phase refrigerant (second refrigerant) flowing through the high-temperature cycle CH. Accordingly, the gas-phase refrigerant is condensed in the intermediate heat exchanger 10, and a high-pressure liquid-phase refrigerant is generated.
The high-pressure liquid-phase refrigerant passes through the low-temperature-side first expansion valve 31, the low-temperature-side receiver 81, and the low-temperature-side second expansion valve 32 in this order. The high-pressure liquid-phase refrigerant is reduced in pressure to a certain extent while passing through the low-temperature-side first expansion valve 31, and becomes a medium-pressure and medium-temperature liquid-phase refrigerant. The liquid-phase refrigerant is stored in the low-temperature-side receiver 81 and is separated into a gas and a liquid. The gas phase component is supplied to the first compressor 2 (specifically, a position upstream of the scroll compressor 22 on the high pressure side) through a low-temperature-side circuit 91 as the gas injection circuit 9. That is, the low-temperature first refrigerant (gas phase component) before being compressed is sent to the first compressor 2 through the low-temperature-side circuit 91.
The medium-temperature and medium-pressure liquid-phase refrigerant that has passed through the low-temperature-side receiver 81 passes through the low-temperature-side second expansion valve 32 and is further reduced in pressure to become a low-temperature and low-pressure liquid-phase refrigerant.
The low-temperature low-pressure liquid-phase refrigerant that has passed through the low-temperature-side second expansion valve 32 flows into the evaporator 1. The evaporator 1 is provided inside the freezing chamber. In the evaporator 1, heat exchange occurs between an air in the freezing chamber and the first refrigerant. It is desirable that the air in the freezing chamber is forcibly sent to the evaporator 1 by a fan. Heat in the freezing chamber is absorbed by the low-temperature liquid-phase refrigerant, so that the temperature in the freezing chamber changes to descend. That is, the freezing chamber is cooled. Correspondingly, the liquid-phase refrigerant flowing through the evaporator 1 increases in temperature and changes from a liquid phase to a gas phase. The refrigerant that has become the gas phase after passing through the evaporator 1 is suctioned into the first compressor 2 again. By continuously performing such a cycle, the temperature of the freezing chamber is adjusted to a desired value.

(Operational Effects)

In recent years, in the field of chillers, it is required to minimize a global warming potential (GWP) value. Therefore, there are often restrictions on the types of refrigerants that can be used. Examples of the low GWP refrigerant include carbon dioxide and the R32 refrigerant mentioned above. On the other hand, in a case where such a low GWP refrigerant is used, an improvement in a cooling capacity of a chiller may be hindered. In particular, this effect is significant in a chiller in which a target temperature is an ultra low temperature of about -45°C to -70°C. Therefore, for example, measures such as increasing a compression ratio of a compressor used in the chiller can be considered. However, in a case where the compression ratio is simply increased as described above, a discharge temperature of the compressor becomes excessively high, and there is a concern that a desired cooling capacity cannot be exhibited.
Therefore, in the present embodiment, the chiller 100 forms the cascade cycle mainly including the low-temperature cycle CL, the high-temperature cycle CH, and the intermediate heat exchanger 10 provided therebetween. Accordingly, compression ratios respectively required for the first compressor 2 and the second compressor 4 can be minimized. As a result, the temperature (discharge temperature) of the refrigerant discharged from these compressors can be further lowered. That is, a cooling capacity of the chiller 100 can be further increased.
Specifically, as shown in Fig. 2, cycle diagrams of the high-temperature cycle CH and the low-temperature cycle CL are superimposed on each other at intermediate positions (intermediate heat exchanger 10). Accordingly, the temperature of the refrigerant can be lowered to a lower temperature compared to a case where only the high-temperature cycle CH is used. For example, in a case where a condenser outlet temperature of the high-temperature cycle CH is 34°C, an evaporation temperature can be set to an ultra low temperature of about -68°C in the low-temperature cycle CL.
In addition, by using the cascade cycle, it becomes possible to use different types of refrigerants in the low-temperature cycle CL and the high-temperature cycle CH. In the low-temperature cycle CL, the mixed refrigerant that contains R32 while mainly containing carbon dioxide is used as the first refrigerant. In the high-temperature cycle CH, carbon dioxide is used as the second refrigerant. As described above, by mainly using the carbon dioxide, it is possible to further increase the cooling capacity compared to a case where only the carbon dioxide is used as the refrigerant, while realizing a low GWP. In addition, in the high-temperature cycle CH, since only carbon dioxide is used as the second refrigerant, an excess decrease in density does not occur compared to a case where R32 is mixed. Accordingly, the compression ratio required for the second compressor 4 can be minimized.
In addition, the gas injection circuit 9 supplies the low-temperature first refrigerant or second refrigerant before being compressed to at least one of the first compressor 2 and the second compressor 4. Accordingly, for example, in a case where the first compressor 2 and the second compressor 4 are configured by a plurality of stages of compressors, a final discharge temperature of the refrigerant can be further lowered by supplying the low-temperature refrigerant to an intermediate position between the plurality of stages.
In addition, according to the above configuration, as the first refrigerant, the mixed refrigerant containing 16 wt% or more and 22 wt% or less of R32 and carbon dioxide is used. Accordingly, it becomes possible to suppress a GWP to 150 or less to be equal to or lower than an international regulation value. As described above, according to the present embodiment, it is possible to provide the chiller 100 capable of achieving both a low GWP and a high cooling capacity.
Furthermore, according to the above configuration, the gas injection circuit 9 is configured to supply the refrigerant to the upstream side of the scroll compressors 22 and 42 on the high pressure side. Here, in the scroll compressors 22 and 42, a configuration is adopted in which the refrigerant flowing through an inside of a casing flows into a compression chamber without being significantly restricted in the flow direction or the like. That is, it can be said that in the scroll compressors 22 and 42, it is easier to add another refrigerant to an outside of the compression chamber than in the rotary compressors 21 and 41. Accordingly, the gas injection circuit 9 can more easily and smoothly add the refrigerant.
More specifically, according to the above configuration, the low-temperature-side circuit 91 and the high-temperature-side circuit 92 as the gas injection circuit 9 are provided in the low-temperature cycle CL and the high-temperature cycle CH, respectively. Accordingly, it is possible to lower the discharge temperature of the compressors (the first compressor 2 and the second compressor 4) in both the low-temperature cycle CL and the high-temperature cycle CH.

(Other Embodiments)

While the embodiments of the present disclosure have been described in detail with reference to the drawings, specific configurations are not limited to the embodiments and include design changes and the like within a range not departing from the gist of the present disclosure.

The chiller described in each of the embodiments is identified, for example, as follows.

(1) A chiller 100 according to a first aspect includes: a low-temperature cycle CL including an evaporator 1 that exchanges heat between an air in a freezing chamber and a first refrigerant, a first compressor 2 that compresses the first refrigerant and supplies the first refrigerant to the evaporator 1, and a low-temperature-side expansion valve 3 that lower a pressure of the first refrigerant that has passed through the first compressor 2; a high-temperature cycle CH including a condenser 5 that exchanges heat between an outside air and a second refrigerant, a second compressor 4 that compresses the second refrigerant and supplies the second refrigerant to the condenser 5, and a high-temperature-side expansion valve 6 that lowers a pressure of the second refrigerant that has passed through the condenser 5; an intermediate heat exchanger 10 that exchanges heat between the first refrigerant flowing from the first compressor 2 and the second refrigerant flowing from the high-temperature-side expansion valve 6; and a gas injection circuit 9 that is provided in at least one of the low-temperature cycle CL and the high-temperature cycle CH and supplies the first refrigerant or the second refrigerant before being compressed to at least one of the first compressor 2 and the second compressor 4, in which the first refrigerant is a mixed refrigerant containing carbon dioxide and an R32 refrigerant, and the second refrigerant is carbon dioxide.

According to the above configuration, the chiller 100 forms a cascade cycle mainly including the low-temperature cycle CL, the high-temperature cycle CH, and the intermediate heat exchanger 10 provided therebetween. Accordingly, compression ratios respectively required for the first compressor 2 and the second compressor 4 can be minimized. As a result, a temperature (discharge temperature) of the refrigerant discharged from these compressors can be further lowered. That is, a cooling capacity of the chiller 100 can be further increased.
In addition, by using the cascade cycle, it becomes possible to use different types of refrigerants in the low-temperature cycle CL and the high-temperature cycle CH. In the low-temperature cycle CL, the mixed refrigerant that contains R32 while mainly containing carbon dioxide is used as the first refrigerant. In the high-temperature cycle CH, carbon dioxide is used as the second refrigerant. As described above, by mainly using the carbon dioxide, it is possible to further increase the cooling capacity compared to a case where only the carbon dioxide is used as the refrigerant, while realizing a low GWP. In addition, in the high-temperature cycle CH, since only carbon dioxide is used as the second refrigerant, an excess decrease in density does not occur compared to a case where R32 is mixed. Accordingly, the compression ratio required for the second compressor 4 can be minimized.
In addition, the gas injection circuit 9 supplies the low-temperature first refrigerant or second refrigerant before being compressed to at least one of the first compressor 2 and the second compressor 4. Accordingly, for example, in a case where the first compressor 2 and the second compressor 4 are configured by a plurality of stages of compressors, a final discharge temperature of the refrigerant can be further lowered by supplying the low-temperature refrigerant to an intermediate position between the plurality of stages.
(2) In the chiller 100 according to a second aspect, the first refrigerant is a mixed refrigerant containing 16 wt% or more and 22 wt% or less of the R32 refrigerant.
According to the above configuration, as the first refrigerant, the mixed refrigerant containing 16 wt% or more and 22 wt% or less of R32 and carbon dioxide is used. Accordingly, it becomes possible to suppress a GWP to 150 or less to be equal to or lower than an international regulation value.
(3) In the chiller 100 according to a third aspect, the first compressor 2 and the second compressor 4 each include a rotary compressor 21, 41 on a low pressure side and a scroll compressor 22, 42 on a high pressure side connected to the rotary compressor 21, 41, and the gas injection circuit 9 is configured to supply the first refrigerant or the second refrigerant to an upstream side of the scroll compressor 22, 42.
According to the above configuration, the gas injection circuit 9 is configured to supply the refrigerant to the upstream side of the scroll compressor 22, 42 on the high pressure side. Here, in the scroll compressor 22, 42, a configuration is adopted in which the refrigerant flowing through an inside of a casing flows into a compression chamber without being significantly restricted in a flow direction or the like. That is, it can be said that in the scroll compressor 22, 42, it is easier to add another refrigerant to an outside of the compression chamber than in the rotary compressor 21, 41. Accordingly, the gas injection circuit 9 can more easily and smoothly add the refrigerant.
(4) In the chiller 100 according to a fourth aspect, the low-temperature-side expansion valve 3 and the high-temperature-side expansion valve 6 each have two expansion valves, the low-temperature cycle CL and the high-temperature cycle CH respectively further include a low-temperature-side receiver 81 and a high-temperature-side receiver 82 provided between the two expansion valves, and the gas injection circuit 9 has a low-temperature-side circuit 91 that supplies the first refrigerant from the low-temperature-side receiver 81 to the first compressor 2, and a high-temperature-side circuit 92 that supplies the second refrigerant from the high-temperature-side receiver 82 to the second compressor 4.
According to the above configuration, the low-temperature-side circuit 91 and the high-temperature-side circuit 92 as the gas injection circuit 9 are provided in the low-temperature cycle CL and the high-temperature cycle CH, respectively. Accordingly, it is possible to lower the discharge temperature of the compressors (the first compressor 2 and the second compressor 4) in both the low-temperature cycle CL and the high-temperature cycle CH.

Industrial Applicability

The present disclosure relates to a chiller. According to the present disclosure, it is possible to provide a chiller capable of achieving both a low GWP and a high cooling capacity.

Reference Signs List

100:: chiller
1:: evaporator
2:: first compressor
3:: low-temperature-side expansion valve
4:: second compressor
5:: condenser
6:: high-temperature-side expansion valve
9:: gas injection circuit
10:: intermediate heat exchanger
21:: rotary compressor
22:: scroll compressor
31:: low-temperature-side first expansion valve
32:: low-temperature-side second expansion valve
41:: rotary compressor
42:: scroll compressor
61:: high-temperature-side first expansion valve
62:: high-temperature-side second expansion valve
81:: low-temperature-side receiver
82:: high-temperature-side receiver
91:: low-temperature-side circuit
92:: high-temperature-side circuit
CH:: high-temperature cycle
CL:: low-temperature cycle
P1:: low-temperature-side pipe
P2:: high-temperature-side pipe

Claims

A chiller comprising:
a low-temperature cycle including an evaporator that exchanges heat between an air in a freezing chamber and a first refrigerant, a first compressor that compresses the low-pressure gas-phase first refrigerant supplied from the evaporator, and a low-temperature-side expansion valve that lower a pressure of the first refrigerant that has passed through the first compressor;

a high-temperature cycle including a condenser that exchanges heat between an outside air and a second refrigerant, a second compressor that compresses the second refrigerant and supplies the second refrigerant to the condenser, and a high-temperature-side expansion valve that lowers a pressure of the second refrigerant that has passed through the condenser;

an intermediate heat exchanger that exchanges heat between the first refrigerant flowing from the first compressor and the second refrigerant flowing from the high-temperature-side expansion valve; and

a gas injection circuit that is provided in at least one of the low-temperature cycle and the high-temperature cycle and supplies the first refrigerant or the second refrigerant before being compressed to at least one of the first compressor and the second compressor,

wherein the first refrigerant is a mixed refrigerant containing carbon dioxide and an R32 refrigerant, and the second refrigerant is carbon dioxide.
The chiller according to Claim 1,
wherein the first refrigerant is a mixed refrigerant containing 16 wt% or more and 22 wt% or less of the R32 refrigerant.
The chiller according to Claim 1 or 2,
wherein the first compressor and the second compressor each include a rotary compressor on a low pressure side and a scroll compressor on a high pressure side connected to the rotary compressor, and

the gas injection circuit is configured to supply the first refrigerant or the second refrigerant to an upstream side of the scroll compressor.
The chiller according to any one of Claims 1 to 3,
wherein the low-temperature-side expansion valve and the high-temperature-side expansion valve each have two expansion valves,

the low-temperature cycle and the high-temperature cycle respectively further include a low-temperature-side receiver and a high-temperature-side receiver provided between the two expansion valves, and

the gas injection circuit has
a low-temperature-side circuit that supplies the first refrigerant from the low-temperature-side receiver to the first compressor, and

a high-temperature-side circuit that supplies the second refrigerant from the high-temperature-side receiver to the second compressor.